A radiation window is a structural element with an opening arranged for electromagnetic radiation to pass through. In most cases a radiation window foil covers the opening, separating for example the inside of e.g. a detector apparatus from its outside. The radiation window foil should absorb the desired radiation as little as possible, but it must simultaneously be strong enough and pinhole-free to withstand and maintain a pressure difference.
FIGS. 1 and 2 illustrate a known method for manufacturing a radiation window. This method has been described for example in the PCT publication number WO2011/151506. The topmost step in FIG. 1 illustrates a carrier 101, at least one surface of which has been polished and faces upwards. An etch stop layer 102 is produced on the polished surface of the carrier 101. If the carrier 101 is made of silicon, advantageous material for the etch stop layer 102 include but are not limited to silicon nitride and silicon oxide. At the third step of FIG. 1, a solid layer 103 is bonded on the etch stop layer 102.
In the fourth step from above in FIG. 1, the solid layer 103 is first thinned into a predetermined thickness and then patterned with a predetermined pattern of differences in thickness. In particular, regularly spaced portions of the originally uniform solid layer 103 are removed to turn said uniform layer into a mesh, a rib of which is illustrated as 104. A conformal diffusion barrier layer 105 is formed on top of the mesh, and a visible light blocking layer 106 is added in the radiation window foil.
In FIG. 2 the starting point is the same at which the first part of the method ended in FIG. 1: on top of a carrier 101 (such as a 6-inch silicon wafer, for example) there exist layers, of which the mesh layer is most clearly visible due to the visible cross sections of the mesh ribs (although also in this drawing the dimensions have only be selected for graphical clarity and are not in scale). In the next step the carrier with the layers on its surface is cut into blanks, of which blank 201 is an example. In the third step of FIG. 2 each blank is glued, soldered, welded or otherwise attached to a radiation window frame or support structure. Of these, support structure 202 is shown as an example. The last step in FIG. 2 shows removing the carrier, which is most advantageously done by etching.
FIG. 3 illustrates an alternative to the first part of the method illustrated in FIG. 1. The method portion of FIG. 3 has also been described in detail in the patent publication number WO2011/151506. The first four steps in FIG. 3 may be similar to those of FIG. 1, with the exception that the etch stop layer may be even thinner than in FIG. 1, for which reason it is referred to as layer 301. The fifth step of FIG. 3 illustrates producing a layer 302, which meanders around the ribs 104 of the mesh and constitutes the main layer of the foil portions that span the openings in the mesh. Further layers, such as a diffusion barrier 105 and/or a visible light blocking layer, can be added on top of layer 302, as is illustrated in the last step of FIG. 3. After that the method illustrated in FIG. 3 continues in conformity with the steps of FIG. 2 explained above.
Despite their numerous advantageous features, radiation windows and window foils produced with the methods of FIGS. 1 to 3 still leave room for improvement in respect of low absorption versus high strength, especially if the opening that the window foil must cover is large.